The invention relates to a coating composition for in situ coating a surface especially a wall formed by plasterboard wall panels to provide a high quality surface finish.
Plasterboard which is referred to in some countries as wallboard, gypsum wallboard, or drywall is widely used to provide internal walls and/or ceilings in building constructions. The plasterboard is cut to a desired size from large panels and the cut lengths are attached to fixtures such as wall bates. The joints between adjacent boards are filled and the surface of the wall is skimmed with a plaster compound by manual trowelling. This is extremely time consuming, labour intensive, and requires considerable skill. In addition, even with such skilled finishing techniques joints and fixing points are often clearly visible through the skin. This is a particular problem when the wall is painted as the painting tends to highlight rather than hide such imperfections.
There is therefore a need for a coating system for coating a surface, especially an erected plasterboard wall or ceiling which will eliminate or at least substantially reduce the problems with known systems.
According to the invention there is provided a coating system for in-situ coating of a surface comprising a dry powder composition which is dispersible in an aqueous applicator medium, the dry powder composition comprising calcium carbonate and, by weight, relative to calcium carbonate, from 4% to 11% of a polymeric binder from 0.60% to 1.5% of a thickening agent and from 0.10% to 0.35% of a surfactant.
Preferably the polymeric binder is an EVA (vinyl acetate/ethylene) binder.
Preferably the surfactant is sodium citrate. Most preferably the thickening agent is an inert mineral thickening agent which may be derived from Attapulgite.
In one embodiment the binder is present in an amount of approximately 5% by weight relative to the calcium carbonate.
In another embodiment the binder is present in an amount of approximately 10% by weight relative to the calcium carbonate.
In one embodiment the surfactant is present in an amount of approximately 0.15% by weight relative to the calcium carbonate.
In another embodiment the surfactant is present in an amount of approximately 0.30% by weight relative to the calcium carbonate.
In one embodiment the thickening agent is present in an amount of approximately 0.63% by weight relative to the calcium carbonate.
In another embodiment the thickening agent is present in an amount of approximately 1.26% by weight relative to the calcium carbonate.
Preferably the coating system includes a preservative/biocide. Most preferably the preservative/biocide is present in an amount from 0.25% to 0.35% by weight relative to the calcium carbonate. Preferably the preservative/biocide is sodium benzoate. Ideally the preservative/biocide is present in an amount of approximately 0.30% by weight relative to the calcium carbonate.
One aspect of the invention provides a coating system for in-situ coating of a surface formed by a plurality of plasterboard sections comprising a dry powder composition which is dispersible in an aqueous applicator medium, the dry powder composition comprising calcium carbonate and, by weight, relative to calcium carbonate, approximately 5% of a polymeric binder, approximately 0.63% of a thickening agent, approximately 0.15% of a surfactant and approximately 0.30% of a preservative/biocide.
Another aspect provides a coating system for in-situ coating of a surface formed by a plurality of plasterboard sections comprising a dry powder composition which is dispersible in an aqueous applicator medium, the dry powder composition comprising calcium carbonate and, by weight, relative to calcium carbonate, approximately 10% of a polymeric binder, approximately 1.26% of a thickening agent, approximately 0.30% of a surfactant and approximately 0.30% of a preservative/biocide.
A further embodiment of the invention provides a method for preparing a dry powder composition comprising the steps of:
preparing a premix comprising the surfactant, the thickening agent and the biocide/preservative; and
adding the premix to at least part of the calcium carbonate and binder.
In a preferred embodiment the method includes the step of dry mixing at least a portion of the calcium carbonate with at least some of the binder and adding the premix to the calcium carbonate/binder mixture. Ideally the method comprises mixing approximately half of the calcium carbonate with the binder, adding the premix and subsequently adding the balance of the binder.
The invention further provides a method for preparing a coating composition especially for application in situ to a wall formed by a number of plasterboard sections comprising the step of mixing a dry powder composition with water.
Preferably the dry powder composition is mixed with water in an amount of approximately 2 kg of coating composition per 1 liter of water.
In one embodiment of the invention the method includes the step of adding a pigment to the mixture. Preferably the pigment is present in an amount of from 0.5% to 5% by weight relative to calcium carbonate.
In addition the invention provides a method of coating a surface formed by a plurality of plasterboard sections comprising applying a coating composition of the invention. Ideally the coating composition is applied by a spray coating technique. Alternatively the coating composition may be applied by a roller technique.